The MARC classification record is an authority record for the classification number(s) and caption contained in field 153 (Classification Number).  Classification numbers with captions may also appear in fields 453 (Invalid Number Tracing) and 553 (Valid Number Tracing).  Index term only records contain an index term in field 154 (General Explanatory Index Term) instead of a classification number and caption in field 153.  Three types of classification numbers are defined in the classification format and identified in 008/07 (Type of classification number):

   Single number - A single classification number is one classification number; the components of which may be contained in a single or repeatable subfield $a (Single number or beginning number of span) in a record.

   Defined number span - A defined number span is a range of classification numbers with a beginning number contained in subfield $a and an ending number contained in subfield $c (Ending number of span).  The numbers between the beginning and ending numbers are defined by a separate table or subarrangement.

   Summary number span - A summary number span is also a range of classification numbers with a beginning and an ending number.  The caption contained in subfield $j (Caption) summarizes a topic that is represented by the span in subfields $a and $c.  A summary number span is not defined by a separate table or subarrangement; instead, the numbers falling within the span are generally defined separately by their own records.

See also:

Classification Data Format:  Introduction